1. Field of the Invention
The present invention relates to a thermal-type airflow meter suitable for measuring the flow rate of air taken into an internal combustion engine, and more particularly to a thermal-type airflow meter, which comprises a housing for protectingly accommodating an electronic circuit therein and a sub-air passage.
2. Description of the Related Art
JP-A 3-233168 discloses an example of prior art thermal-type airflow meters. In this prior art, a housing part for protecting an electronic circuit therein and a sub-air passage part are arranged in the same plane to be made one body. Further, there is also proposed an airflow meter, in which a housing and a sub-air passage are plastic-molded as a unitary body.
However, the prior art as mentioned above needs to be improved in the following respects:
(1) A member in which a housing and a sub-air passage are formed should be suitably shaped for assembly by means of insertion technology (that is, should have proper dimensions to match an inserting hole); PA1 (2) The relative positioning of a housing and a sub-air passage should never vary. That is, after the sub-air passage has been fixedly attached to a member in which a main air passage is formed, the attached position of the subair passage should never vary; PA1 (3) The deformation of an airflow meter due to the environmental operating conditions as small as possible, and the durability and reliability thereof should be sufficient; and PA1 (4) There should be freedom in designing the shape of a sub-air passage, and further even if it has the complicated shape, it can be easily manufactured.